SLINGERLANDS – Albany County released an engineer’s report that discussed the causes of the July 12 collapse of the new County Rail Trail Bridge over Route 85 in Slingerlands on Thursday, Sept. 7 after refusing to release it in August, according to the Times Union.
The County commissioned the report, which was completed on August 4, to determine what caused the collapse.
The report found that the new bridge’s unique design placed added stress on transition points in the girders. Girders, the long pieces of steel which make up the sides of the bridge and help support its deck, buckled as concrete was being poured into it.
The unusual design was meant to mimic the old span, which was built in the early 1900’s, and included a step design where the ends of the girders are thinner then transition to a thicker profile across the middle of the span.
The five-page report, completed by Brett Reynolds of Colliers Engineering and Design, noted that the engineering firm that designed the bridge, M.J. Engineering and Land Surveying, did not take into account that the design would put added stress on the girders.
In Reynolds’ report, the unique design of the two girders used to help support the bridge’s span, but had stress points in two locations where at the top of the girder, called a flange, had transitioned from deeper to shallower sections. Meaning, that the transition went in a “step” configuration from horizontal to vertical.
“The abrupt compression flange transition in the step pattern at the bridge can result in a concentration of stresses being imparted into the web at the location of the transition,” the report said. “It does not appear this additional stress concentration in the webs at the transition locations were considered. As the web and vertical stiffeners are consistent across the entire length of the girder, it does not appear that the design accounted for this additional stress concentration at the webs at the step location.”
In addition, Reynolds added that it does not appear that the construction means and methods were the cause of the collapse.
But other factors may have contributed to the failure. An inspection at the fabricator of the girders also found problems with design when they were manufacturing the steel spans.
“It appears that the shop inspection identified geometry issues during the fabrication of the girders. Additional stresses from beam fabrication (eventually approved by designer) could have contributed to the overall stresses that eventually led to the failure,” the report said.
Determining who pays for the replacement.
Albany County is currently discussing with insurance companies as it needs to seek reimbursement of approximately $600,000 to cover the cost and removal of the damaged bridge and the leasing and installation of a new temporary bridge. The new bridge will have to be redesigned and fabricated and it is estimated that it will take more than a year to get the permanent span in place.
The project originally began in March to raise the low-lying bridge over New Scotland Road and Route 85. The span was hit by trucks frequently causing DOT to shut down the road.
Construction of the temporary steel bridge will begin Monday, Oct. 2, and is slated to be completed by Tuesday, Oct. 31. The county will also install a pedestrian railing along the sidewalk of the road.
The pedestrian and bicycle detour will remain in place for the rail trail until bridge construction is complete.
This story appeared on page 2 of the September 13, 2023 print edition of the Spotlight